Electric vehicles or hybrid vehicles include a converter that converts a DC voltage provided by a battery arrangement into at least one AC voltage required by an electric motor that drives the vehicle. The battery arrangement includes a number of battery cells, which are usually rechargeable cells, such as lithium-ion cells.
According to a first known concept, a number of battery cells are connected in series, where a DC supply voltage is provided by this series arrangement. A DC/AC inverter receives the DC supply voltage and generates an AC supply voltage from the DC voltage. Here, the inverter has to be adapted to compensate for voltage variations occurring in the DC supply voltage. Such voltage variations may occur due to discharging the battery cells during operation.
According to a second known concept, a DC/DC converter is connected between the battery arrangement and the DC/AC inverter. The DC/DC converter is adapted to provide a constant DC supply voltage to the DC/AC inverter, and therefore compensates for voltage variations in the voltage provided by the battery arrangement. However, providing the DC/DC converter adds to the complexity of the system.
Most types of accumulator cells, such as lithium-ions cells, should not be discharged below a lower voltage limit, in order to prevent degradation or damage. In order to prevent improper discharging of individual accumulator cells cell-balancing schemes can be applied. Such balancing schemes involve discharging more highly charged cells to the benefit of less charged cells. Circuit arrangements for performing cell balancing schemes are required in addition to the DC/AC inverter.